Billions of containers and packaging products are manufactured each year for packaging food and beverage products and other household items. Various materials are used to manufacture these containers, depending on the particular use or application. Container manufacturers and food and beverage marketers must balance the design requirements for a packaging application against the economics of producing a given container. Design requirements may often include visually perceptible container properties such as surface gloss and reflectiveness, the clarity of the container wall, and the transparency and haze level of the container wall material. These visual properties have importance in the selection of a cost-effective packaging material for both functional and aesthetic reasons. The aesthetic elements of a packaging material choice may also be driven by consumer preference, because ultimately the consumer""s decision to purchase a packaged product, for example a food or beverage, can be influenced by the appearance of the container. The functional aspects of these visual properties generally relate to container and/or product inspection, especially inspection of filled containers.
Glass containers are widely used and have properties of transparency and clarity, with little or no haze. These visual properties of glass will generally satisfy the functional and aesthetic requirements for a given container use. Glass containers also have gas barrier properties as well as heat resistance, making them suitable for packaging carbonated soft drinks and beer, as well as perishable products that are sensitive to oxygen and products which must be sterilized or hot-filled into containers at temperatures of 85xc2x0 C. or more. The initial cost of glass containers is low, however, the efforts to recycle used glass containers have been hampered by the transportation expense involved in transporting the heavy glass containers to a recycle facility. These transportation expenses are also a cost factor when the glass containers are shipped to the user or when they are filled with new products and shipped to their point of sale. Moreover, glass containers are susceptible to breakage and inconvenient to handle.
On the other hand, containers made from plastic are often chosen by consumers and packagers due to their combination of light weight, durability and shatter resistance. Plastic containers may be formed from a variety of different polymers. Depending on the polymeric material selected, certain properties of the container may be achieved such as gas or water vapor barrier properties, impact strength, transparency and heat resistance.
Polyolefins such as polyethylene and polypropylene have barrier properties against water vapor, yet they are generally unsatisfactory from the standpoint of transparency and gloss. Polyvinyl chloride has gas barrier properties and is satisfactory in terms of transparency, but has inferior heat resistance. Polycarbonate has good transparency and sufficient heat resistance to withstand steam sterilization but does not have good gas and water vapor barrier properties.
Polyethylene terephthalate (PET) is widely used in the manufacture of containers for its excellent transparency and impact strength. In certain applications, polyethylene terephthalate also has satisfactory barrier properties against water vapor and gasses.
Polyethylene terephthalate is a crystallizable polymeric material which may exist in either an amorphous state or a crystallized state, or in a combination of both the amorphous and crystalline states. When heated to a temperature above its glass transition temperature and below its melting point, polyethylene terephthalate undergoes a transition from its amorphous state to its crystalline state, although this transition does not occur instantaneously. Similarly, when cooled slowly from its melting point to its glass transition point, polyethylene terephthalate undergoes crystallization, a transition from the amorphous phase to the crystalline phase. This transition does not occur instantaneously either, and substantially amorphous polyethylene terephthalate may be obtained by rapidly quenching from the melt, as is disclosed in U.S. Pat. No. 4,414,266 to Archer, et al.
Crystallization upon heating of a crystallizable polyester may be due to the further growth of existing crystals in the polymer or to the formation of new crystals, or both. Many physical and chemical properties of the polyester material change as the level of crystallinity increases and a variety of techniques are used to characterize the amount of crystallinity in a polymer. The crystallinity may be observed directly, for example by optical or electron microscopy techniques, or can be inferred by refraction techniques.
The crystallization behavior of polyesters such as polyethylene terephthalate is often determined by either a specific heat vs. temperature curve or a differential scanning calorimeter (DSC) curve, or both, for a sample of the polymer. At a temperature higher than the glass transition temperature (Tg), crystallization takes place, which is demonstrated both by a sharp drop in the specific heat curve and also by a sharp upward peak in the differential scanning calorimeter curve. The crystallization onset temperature of a polyester determined by differential scanning calorimetry is that temperature at which the exothermic crystallization reaction begins, or the beginning of the rise toward the peak of the exothermic crystallization reaction curve. The peak crystallization temperature of a polyester determined by differential scanning calorimetry is that temperature at which the exothermic crystallization reaction peaks. The crystallization onset temperature and the peak crystallization temperature determined by differential scanning calorimetry are both located in the range between the glass transition temperature and the melting temperature (Tm) of the material and they are both dependent upon polymer chain length and composition, and the heating rate.
Amorphous phase polymer chains may be axially or bi-axially oriented by applying force, in either one or two directions, respectively, to the polymeric material while it is above its glass transition temperature. Products such as biaxially oriented flat film and shaped objects such as cups thermoformed from flat sheet exhibit improved mechanical properties including dimensional stability, heat resistance and strength resulting from stretching and/or shaping at temperatures above Tg.
Characterization of the uniaxial drawing properties of PET sheet at processing temperatures above Tg illustrates that the material yields in a controlled and uniform manner at such temperatures. At higher strain levels, i.e. draw ratios, the stress increases sharply and strain hardening occurs prior to rupture. Developing strength and rigidity via strain hardening is important in applications such as manufacturing containers for carbonated soft drinks and PET processing temperatures on the order of 85-100xc2x0 C. are often used in such processes. If the resin temperature in such a process is increased to above 110xc2x0 C., the polymer flows more and a much higher stretch is required to achieve a given degree of strain hardening. The amount of orientation attained at this higher stretch is less than that obtained at the same stretch ratio at lower temperatures. This results in lower strength in the hot stretched polymer, although shrinkage is reduced, presumably because of the lower degree of orientation.
Another process variable affecting properties in the stretched polymer is the strain rate. At high strain rates there is considerable molecular resistance to chain disentanglement and movement. Strain hardening will occur at lower stretch ratios as the strain rate is increased. Also, at high strain rates a higher degree of crystallinity is achieved in the product. Increased crystallinity results in product rigidity but at higher levels can result in brittleness and a resistance to molecular movement which may adversely impact product properties and the ability to be further processed.
Thus, polyester containers formed by biaxial orientation blow molding of preforms or parisons may have excellent strain induced rigidity and mechanical strength properties resulting from the strain induced orientation and strain induced crystallinity occurring in an optimized blow molding process. This strain induced orientation and strain induced crystallinity of the polymer chains is fixed in the polymer at room temperature. However, because the glass transition temperature of polyethylene terephthalate is about 70xc2x0 C., when biaxially oriented containers of polyethylene terephthalate are used in a standard hot filling application with temperatures of at least about 85xc2x0 C., the strain orientation in the softened polymer is released. When the biaxially oriented polyethylene containers are heated above their Tg, the strain oriented, straightened polymer molecule chains tend to reacquire their natural coil shape, which causes the blow molded container to shrink and distort.
Furthermore, if PET preforms or containers are heated to a temperature substantially above Tg, especially temperatures in excess of the normal 100xc2x0 C. upper limit for processing PET discussed above, after a brief period of time (depending on the temperature) a visually perceptible whitening or hazing of the polymer occurs as a result of heat-induced crystalline growth.
U.S. Pat. No. 5,261,545 to Ota, et al. discloses a method for producing a biaxially oriented blow molded polyester resin container, in which only those portions of the container such as the neck and the bottom portions which are not substantially subjected to orientation in the blow molding process are heated and then annealed so as to increase the density of spherulite texture in those portions. The process improves the thermal resistance, stiffness and content resistance to the same extent as that which exists in the oriented cylindrical sections of the container, where the polymer molecules have been biaxially oriented. The container is disclosed as suitable for hot filling.
In the Yoshida, et al. U.S. Pat. No. 5,068,136, it is reported that heat set technology has been developed for heat setting polyethylene terephthalate containers by holding a wall portion of the blow molded container under heat treatment at 100-130xc2x0 C. to remove residual strain, and that there also has been developed a technique of crystallizing and whitening the open end portion of the container with hot air or a heater. It is disclosed that these processes have resulted in heat resistant polyethylene terephthalate containers capable of being hot filled with contents having a temperature of as high as 85xc2x0 C. However, these techniques are complicated and require substantial processing time and additional capital investment for heated molds.
U.S. Pat. No. 4,711,624 to Watson discloses an apparatus for making open ended thermoplastic tubular articles which are dimensionally stable at elevated temperatures. An open ended polymer tube is placed between a fixed, heated external mold and a cooled mandrel, which is vertically displaceable relative to the mold, and both ends of the polymer tube are clamped to restrain the polymer tube axially. The polymer tube is radially expanded into contact with the hot mold and maintained in contact for a sufficient time to ensure dimensional stability, and then allowed to shrink back into contact with the cooled mandrel. The mandrel is maintained at a temperature below the glass transition temperature of the polymer. It is disclosed that for manufacturing containers made of polyethylene terephthalate for food or beverage use, a suitable heat setting temperature for the mold is from 150-230xc2x0 C., for a time period on the order of 5 seconds and with an applied pressure of at least 3.4 bars.
U.S. Pat. No. 5,445,784 to Sugiura, et al. discloses a multi-step process for making a heat resistant PET bottle beginning with heating the preform and blow molding it into a hot mold to form a primary intermediate molded bottle shaped piece, heating that primary piece to a higher temperature to form a secondary intermediate molded bottle shaped piece, and blow molding that secondary piece into a mold heated to a temperature that is hotter than the anticipated maximum service temperature for the heat resistant container. The container is disclosed as having no stress remaining from the biaxial orientation blow molding process.
U.S. Pat. No. 4,803,036 to Maruhashi, et al. reports that there are multi-step heat setting processes for improving the heat resistance of polyester containers, and a method in which heat setting is carried out simultaneously with draw-blow-forming in a blow-forming mold is considered preferable because of low equipment cost and the process having fewer steps. However, the manufacturing speed of this process is still low because of the relatively long residence time in the mold necessary for heat setting after the draw-blowing operation as well as cool down time prior to withdrawal of the container. According to the Maruhashi, et al. patent, in the process for the preparation of a hollow formed body wherein draw-blow-forming and heat setting of the molecular orientation are carried out simultaneously, it is expected that if the preform being draw-formed is maintained at as high a temperature as possible, heat setting will be possible while the preform is being draw-formed and the residence time of the formed container in the mold will be drastically shortened. However, preheating of the amorphous preform at a high temperature causes problems such as thermal deformation of the preform and thickness unevenness at the draw forming step. Also, whitening and reduction in drawability are caused by thermal crystallization of the polyester. U.S. Pat. No. 4,803,036 to Maruhashi, et al. discloses that by maintaining a hollow-forming mold, a polyester preform and air to be blown into the preform at predetermined levels, respectively, and using a high speed drawing process to draw the preform, the temperature of the preform becomes higher than the temperature of heat by internal friction or the temperature of heat by crystallization, and drawforming and heatsetting proceed simultaneously and a container with resistance to contraction is obtained at a high manufacturing speed. It is disclosed that the higher the drawing speed, the lower the amount of thermal contraction in the formed container when hot filled at 88xc2x0 C. It is also disclosed that the higher the preform temperature, the lower the amount of thermal contraction in the formed container when hot filled. However, U.S. Pat. No. 4,803,036 discloses that when such a preform is heated to 115xc2x0 C., the preform becomes crystallized and whitened, and also the formed bottle whitens. Furthermore, because the blowforming was performed while the preform was softened by the high temperature, thickness unevenness resulted as the axis of the bottle deviated from the axis of the preform. Accordingly, the thin portion of the bottle was readily deformed when hot filled. The thermoplastic polyester in U.S. Pat. No. 4,803,036 is disclosed as being composed mainly of ethylene terephthalate units as well as modified polyethylene terephthalate resins containing lower than 2% by weight of diethylene glycol.
U.S. Pat. Nos. 5,344,912, 5,346,733 and 5,352,401 to Dalgewicz III, et al. disclose a polyester article having a linear dimensional shrinkage between about 0% and 6% when heated from about xe2x88x9260 to about 200xc2x0 C. as well as good gas barrier properties, obtained from a xe2x80x9cmelt-to-moldxe2x80x9d process. The shaped polyester article is prepared by heating a composition of a substantially non-oriented crystallizable thermoplastic polyethylene terephthalate homopolymer to an amorphous state and maintaining the composition at a temperature above its peak crystallization rate temperature and contacting the composition with a shaping surface at or above that temperature for a time sufficient to provide a crystalline composition having an enthalpy of recrystallization of about 0.0 to about xe2x88x922.1 calories per gram. The shaped article is then cooled at a rate of from about 5xc2x0 to about 80xc2x0 C. per minute. No haze or transparency values are reported for the polyester articles produced by the process.
Heat resistant materials may be used to form containers, such as the bottle disclosed in U.S. Pat. No. 5,102,705 to Yammoto, et al. which is made of polyethylene naphthalate resin and formed by stretching a preform so that the specific stretch index is 130 cm or more. The polyethylene naphthalate resin used for forming the bottle has 60 mole percent or more ethylene-2,6-naphthalate units and has a Tg of about 120xc2x0 C. or more. However, polyethylene naphthalate resins have a much greater cost than polyethylene terephthalate resins, so such a bottle is expensive to produce.
Often, as an alternative to employing complex processing techniques requiring added production time and/or additional capital outlay for special processing equipment or utilizing a high cost material in order to enhance the barrier, high temperature, or other performance characteristics of monolayer containers, multi-layer structures have been proposed to obtain the benefits of at least two different polymers in a single application. A layer of a polymer having heat resistance, high strength, and/or barrier properties, etc., may be added to the structure to produce a multi-layer laminate with improved properties. Combining layers of different polymers is a method generally used to form a multilayer laminate which takes advantage of the different properties which may be available in the different polymer layers while also using less of the more expensive polymer than if an entire container was manufactured from it.
Multilayer laminates, containers and other articles have numerous applications in industry, particularly for packaging applications. Kirk-Othmer Encyclopedia of Chemical Technology, Third edition, Volume 10, page 216 (1980), Wiley-Interscience Publication, John Wiley and Sons, New York, details generally the materials and processes required for making such articles as well as their applications. Another article of interest, for example, is xe2x80x9cFilms, Multilayer, xe2x80x9d by W. Schrenk and E. Veazey, Encyclopedia of Polymer Science and Engineering, Vol. 7, 106 (1980). Generally, such articles are prepared by coprocessing individual polymers in injection or extrusion operations or by laminating individually formed layers together or by a combination of these processes. Coprocessing as discussed herein refers to forming and/or subsequently processing at least two layers of polymeric material. Common polymers used in these applications include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polycarbonate, polystyrene, acrylonitrile copolymers and the like. Desired properties in the laminates, films, sheets and the like, depend on the intended applications but generally include good mechanical properties such as tensile and impact strengths, processability, tear resistance, gas barrier properties, moisture barrier properties, optical properties, thermal and dimensional stability and the like.
However, the processes which may be used to shape multi-layer laminates, for example producing a container by one of the many available blow molding methods, often become more complex and unpredictable when multi-component polymeric materials are used such as blended resins and/or laminates.
Such methods of forming useful articles from multi-layer laminates often require that each layer of the laminate be stretched, expanded or extended in one or more directions, or deformed in some other way. This stretching, extending or other deformation may be carried out concurrently with the processing of forming the laminate or individual layers from the melt or may be part of a subsequent forming operation. Such methods of forming include but are not limited to, uniaxial and biaxially stretching of extruded films, thermoforming of multilayer laminates, blowing of extruded or injection-molded tubes and stretch blow molding of preforms or parisons.
Subsequent forming operations usually require the application of heat such that all of the layers are heated to above their Tg. For example, many methods of container formation require uniform stretching or expansion of the multilayer laminate at temperatures sufficient to stretch any polymeric material present in the laminate. It is advantageous to be able to coprocess the laminate, for example, to stretch or expand it without fracturing, tearing or otherwise destroying the integrity of any layer by creating defects within the layer. The creation of crystallinity in a layer of the laminate such that visually perceptible haze occurs and/or formability and stretchability are impacted may be considered a defect, depending on the particular application of the laminate.
U.S. Pat. No. 3,869,056 to Valyi discloses that whenever it is difficult to satisfy all of the requirements and specifications for a container by using a single plastic, a lined container, wherein the container wall is composed of more than one substance provides properties that no single plastic possesses.
U.S. Pat. Nos. 5,364,669 and 5,405,565 to Sumida, et al. both disclose composite films comprising a layer of liquid crystal polymer having gas barrier properties, an adhesive layer, and a thermoplastic layer formed from thermoplastics such as polyalkylene terephthalates, olefin polymers, nylons, polycarbonates and the like. The composite films are suitable as a food packaging material. Sumida, et al discloses that molten liquid crystal polymer may be biaxially stretched from the melt but should be extruded downward from the die to prevent the problems associated with low melt viscosity and weakness of the melted film which create difficulties when the molten liquid crystal polymer film is extruded upward from the die. Examples of the Sumida, et al. process are provided wherein Vectra7 A900 (a trademark of Hoechst Celanese Corporation of Somerville, N.J.) wholly aromatic liquid crystal polyester resin is extruded at 2901C at a blow ratio of 5.5 and a draft ratio of 6.0 to obtain a multiaxially oriented liquid crystal polymer film. Blow molding and stretch blow molding to obtain bottles or jars are not disclosed.
U.S. Pat. No. 5,326,848 to Kashimura, et al. discloses thermotropic liquid crystal polyesters produced by a hybrid copolymerization process wherein polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or copolymers of PET and PEN are combined with conventional liquid crystal polyester structural units based on hydroxy naphthoic acid and hydroxy benzoic acid, or units based on hydroxy naphthoic acid alone. Kashimura, et al. proposes to achieve both excellent formability and gas barrier properties and discloses laminates having layers of the liquid crystal polyester compositions with layers of other polymers such as polyesters, polyolefins and polyamides to produce laminated containers such as cups and bottles. A polyester composition capable of preparing formed shapes by deep drawing an unstretched sheet is disclosed as comprising PET combined with units based on hydroxy naphthoic acid and hydroxy benzoic acid. However, it is disclosed that the gas barrier property of this deep drawing composition may sometimes be inferior to the gas barrier properties obtained by the other compositions disclosed which are not disclosed as suitable for deep drawing. In all of the liquid crystal polyester compositions disclosed by Kashimura, et al., an aliphatic dihydroxy component must be present in at least 15 mol percent in the liquid crystalline polyester. Although the formation of bottles and blow molding are disclosed, neither are demonstrated, nor are draw ratios for bottle formation or blow molding disclosed. Biaxial stretching of a film of the composition heated to 1001C to 2401C at a ratio of 3xc3x973 is disclosed.
Other stretchable multilayer laminates and articles comprising an LCP layer have been proposed. For example, JP 5,177,797 A discloses that multilayer containers may be prepared from a laminate comprising layers of a thermoplastic resin and an LCP. Other disclosures of similar nature and of interest include, for example, JP 5,177,796 A; JP 1,199,841 A; JP 5,169,605 A; and WO 9,627,492 A.
U.S. Pat. No. 3,955,697 to Valyi discloses a heat resistant container with a barrier layer entrapped between two layers of a heat resistant plastic such as acetal polymers, polycarbonates, phenoxy resins, polysulfones, polyolefms, polyimines or ionomeric resins. The outer and inner layers may be the same or different. The barrier material is selected from the group consisting of polyvinylidene chloride, polyvinyl acetate, acrylonitrile polymers and methacrylonitrile. Valyi discloses that the liner is prepared from a laminate or sandwich so that in the resultant container the barrier layer is entrapped between two layers of a heat resistant plastic. In use, when the container of the present invention is exposed to elevated temperatures, the low melting layer entrapped between the heat resistant layers may, and probably will, soften, if not melt, depending upon the hot use temperature. However, because the low melting layer is entrapped and in substantial conformity with the adjoining protective layers, it lacks mobility and must remain in place. Thus, upon cooling, the lower melting layer will be restored to its normal condition without change.
Okudaira, et al. disclose in U.S. Pat. No. 4,535,901 and UK Patent Application GB 2091629A that in the case of successive injection laminate molding of a multi-ply parison, a molten crystalline thermoplastic resin which forms the inner layer, particularly a polyethylene terephthalate, is solidified in a transparent amorphous state by quenching. However, when the middle or the outer layer is formed subsequently as a molten resin, it is difficult to quench because the molten resin flows on the surface of the inner amorphous resin layer or the middle layer (in the case of the formation of the outer layer) and is cooled through the inner layer or both the inner and middle layers, and hence, the interfacial part of the layers becomes opaque due to heat crystallization of the resins of both layers. This interfacial crystallization disclosed by Okudaira, et al. not only causes deterioration of the blow moldability of the resulting multi-ply injection molded parison but also other disadvantages such as lowering of the interfacial adhesion between both resins and deterioration of the physical properties of the blow molded container. Okudaira, et al. discloses that in the formation of a multi-ply parison by injection molding, each resin should be injected and laminated to each other within a very short period of time and hence, even if a crystalline resin such as polyethylene terephthalate is used, the resin can be quenched without giving enough time to crystallize at the interfacial region. Thus, a high transparency, multi-ply parison is obtained. Three and five layer containers having innermost and outermost layers composed of thermoplastic polyester are preferred. Containers having heat resistance due to a central layer of polycarbonate and good barrier properties due to a central layer of metaxylylene group-containing polyamide are disclosed.
U.S. Pat. No. 4,550,043 to Beck reports that the method of Okudaira, et al. results in a preform having such a thick layer of central barrier material as to be economically unfeasible and discloses a five layer injection molded preform for forming blow molded containers having inner and outer first layers of a thermoplastic resin, thin inner and outer layers of a barrier material next to and between the inner and outer layers of thermoplastic resin, and a central layer of high temperature thermally stable material such as polycarbonate or acrylonitrile.
U.S. Pat. No. 4,847,129 to Collette, et al. reports that the preform disclosed by Beck in U.S. Pat. No. 4,550,043 has a core formed from a high temperature stability thermoplastic which is the major portion of the preform, and discloses a process of forming an injection molded preform for a container which is formed primarily of PET or similar saturated polyesters which are to be utilized in the packaging of hot fill liquids. The preform is of a laminated construction with the body of the preform being a five layer construction and the neck of the preform being primarily of a three layer construction including outer layers of PET and a core formed of a high Tg polymer. The same high Tg polymer that forms the core of the neck is present in the form of two thin layers in the body of the preform and located between the inner and outer layers and core of the body, which may be formed from PET. The high Tg polymer may be polyethylene naphthalate, polycarbonate, polyarylate or other commercially available polymers with a Tg""s in excess of 90xc2x0 C.
U.S. Pat. No. 5,035,931 to Yamada, et al. discloses a multi layer parison with a nine layer structure in the mouth section, with five of the layers being heat resistant resin layers such as polycarbonate, polyarylate, polyethylene naphthalate, polyacetal, polysulfone, polyether etherketone, polyethersulfone, polyetherimide, polyphenylenesulfide, blend polymers of these resins and blend polymers of one or more of these resins with polyethylene terephthalate. The other resin layers may be polyethylene terephthalate or another thermoplastic polyester or copolyester. The Yamada, et al. patent teaches away from the use of a heat resistant resin in the side wall portion of the container and discloses that the heat resistance in this portion of the container may be achieved by stretching and heat setting.
Multi-layered parisons of polyethylene terephthalate having barrier layers of a xylylene group-containing polyamide (MX nylon) resin to improve gas barrier properties are disclosed in U.S. Pat. No. 4,501,781 to Kushida, et al. and U.S. Pat. Nos. 4,728,549, 4,816,308, 4,868,026 and 4,994,313 to Shimizu, et al. However, the Shimizu, et al. patents disclose that the MX nylon resin has a poor affinity to thermoplastic polyesters such as polyethylene terephthalate. This defect is confirmed in the Yoshida, et al. U.S. Pat. No. 5,068,136, which reports that the five layered container disclosed in U.S. Pat. No. 4,728,549 to Shimizu, et al. undergoes delamination between the MX nylon containing layers (the two intermediate layers) and the layer of polyester (the innermost, central, and outermost layers) when an impact works on the container. This results in a loss of transparency at that portion of the container which undergoes interlayer delamination. U.S. Pat. No. 5,068,136 to Yoshida, et al. also reports that the container disclosed in U.S. Pat. No. 4,501,781 to Kushida, et al. has insufficient transparency and suffers container deformation and leakage when hot-filled at 85xc2x0 C.
U.S. Pat. Nos. 4,743,479 and 4,774,047 to Nakamura, et al., disclose multi-layered containers of polyethylene terephthalate having a central heat resistant layer of a polyarylate polyethylene terephthalate resin or a polycarbonate resin. In U.S. Pat. No. 5,068,136 to Yoshida, et al., it is reported that polymers alloys obtained by melt blending polyethylene terephthalate and polyarylate have been used to form heat resistant containers, but that the moldability and barrier properties are degraded. Multi-layer containers using layers of polyarylate and polyethylene terephthalate resins such as those disclosed in U.S. Pat. Nos. 4,743,479 and 4,774,047 to Nakamura, et al., are reported as having poor oxygen barrier properties by U.S. Pat. No. 5,068,136.
U.S. Pat. No. 5,068,136 to Yoshida, et al. discloses a five-layered container formed by biaxial orientation blow molding of an injection-molded, five layered-structured parison. The central, innermost and outermost layers are a polyester resin containing ethylene terephthalate as a main recurring unit. The two intermediate layers between the innermost layer and the central layer and the outermost layer and the central layer comprise a resin B. Resin B comprises a mixture of a polyester resin containing ethylene terephthalate as a main recurring unit together with polyarylate or a resin produced by an ester exchange reaction of the polyester resin with polyarylate, and a m-xylylene group containing polyamide. It is disclosed that the injection molded parisons were heated to a surface temperature of 100-110xc2x0 C., transferred to a container mold, and blow molded to yield a container having 4.45% haze and a volume contraction ratio of 1.2% at 85xc2x0 C. It is also disclosed that modifying the polyethylene terephthalate resin of the central, innermost and outermost layers with 5% MX nylon results in a blow molded container having 19.7% haze and a volume contraction ratio of 1.6% at 85xc2x0 C.
U.S. Pat. No. 5,115,047 to Hashimoto, et al., discloses that a copolyester mainly derived from isophthalic acid units having a high glass transition temperature and excellent thermal resistance is desirable and avoids the problems associated with obtaining an isophthalate containing copolyester by dry blending dried polyethylene terephthalate resin with a dried isophthalate-type copolyester having a low Tg. Specifically, the high Tg isophthalate-type copolyester is derived from dicarboxylic acid units composed of 95-60 mole % isophthalic acid units and 5-40 mole % of 2,6-napthalenedicarboxylic acid units and dihydroxy compound units composed of 95-70 mole % of ethylene glycol units and 5-30 mole % of 1,3-bis(2-hydroxyethoxy)benzene units. The high Tg isophthalate-type copolyester, in an amount of 5-50 per cent by weight, may be combined with 50-95 weight % of polyethylene terephthalate to form a polyester composition having a Tg of 75-85xc2x0 C. The polyethylene terephthalate that is combined with the copolyester to form a polyester composition may contain 10-20 mole % of dicarboxylic acid units or ethylene glycol units other than terephthalic acid and ethylene glycol, respectively. Both the isophthalate-type copolyester and the blend of PET/isophthalate copolyester may be laminated to layers of polyalkylene terephthalate, preferably polyethylene terephthalate. If the high Tg isophthalate-type copolyester has an isophthalic acid content of more than 95 mole per cent, the resulting copolyester does not have a sufficiently high Tg, if the isophthalic acid content is less than 60 mole percent, the Tg of the resulting copolyester is too high and a blend of the high Tg isophthalate-type copolyester and polyethylene terephthalate, or a multi-layer laminate of the copolyester cannot be stretched sufficiently. A polyester container may be produced by the biaxial stretch blow molding method from an injection molded or extruded preform at a stretching temperature of 80-120xc2x0 C. To improve the rigidity of the polyester container, a layer of polyethylene terephthalate may be laminated to the inside and outside layers of the polyester composition. Although excellent transparency and thermal resistance are disclosed by the Hashimoto, et al. patent for its laminated preforms and laminated blow molded articles, no hot fill shrinkage values were reported for stretch blow molded bottles.
U.S. Pat. No. 5,213,856 to Po"", et al. discloses amorphous copolyesters wherein the acid component is derived from 50% to 80% by mole of isophthalic acid or a derivative thereof and 50% to 20% by mole of 2,6-naphthalene dicarboxylic acid or a derivative thereof. The copolyesters have oxygen barrier properties and a Tg greater than or equal to 73xc2x0 C. They may be coextruded between two or more layers of other polymers and formed into hollow containers.
U.S. Pat. No. 5,006,613 to Shepherd, et al., discloses blends of polyethylene terephthalate and polyethylene naphthalate and a compatibilizing amount of a copolyester having a high Tg and suitable for forming hot fill containers having less than 10% haze. Laminates are not disclosed.
U.S. Pat. No. 4,874,647 to Yatsu, et al. discloses that a transparent polyethylene terephthalate having a sufficient heat resistance to withstand a hot filling operation while maintaining transparency has never been available. It is reported that prior methods for obtaining heat-resistant hollow containers from polyethylene terephthalate, including: (1) lamination of a heat-resistant resin such as polyarylate, (2) molding followed by heat setting, and (3) treatment of molded containers with a solvent to improve crystallinity, all impart heat resistance to the polyethylene terephthalate by using by using special molding means or by applying a treatment after molding. The Yatsu, et al. patent reports that containers produced by these methods were unsatisfactory in heat resistance and transparency when hot filled with juice. U.S. Pat. No. 4,874,647 to Yatsu, et al. discloses a heat resistant polycarbonate/polyester composition comprising 20-80 weight % polyalkylene terephthalate and 20-80 weight % bisphenol-A polycarbonate, the composition having a single glass transition temperature of from 80-130xc2x0 C. A layer of the polycarbonate/polyester material may be laminated to a layer or layers of a polyalkylene terephthalate material having a Tg of from 50-120xc2x0 C. The layer of polyalkylene terephthalate material contains from 50 mole per cent to 100 mole per cent terephthalic acid units and may contain a minor proportion of aromatic dicarboxylic acid units other than terephthalic acid such as isophthalic acid, phthalic acid and naphthalene dicarboxylic acid. The laminated material may be formed by melt-coextrusion into a preform and stretched blow molded to form hollow containers for hot fill applications. The haze level of a press molded specimen of the high Tg isophthalate-type copolyester is disclosed as 5.6% for a 70/30 weight ratio polyethylene terephthalate/polycarbonate composition having a Tg of 84xc2x0 C. As the amount of polycarbonate is increased in order to increase the Tg of the high Tg isophthalate-type copolyester, the haze values increase to greater values. No haze values are disclosed for stretch blow molded laminates having a polyalkylene terephthalate layer and a high Tg isophthalate-type copolyester layer.
U.S. Pat. No. 4,327,137 to Sawa, et al. discloses a heat resistant container formed by direct blow molding prior to solidifying, after co-extruding by a method of intra-die laminating at least one layer of polycarbonate and at least one layer of a thermoplastic polyester without the use of an adhesive tie layer. It is disclosed that the transmission of parallel light for direct blow molded bottles is between 82-83%.
U.S. Pat. No. 4,414,230 to Hannabata, et al. discloses a plastic container having gas barrier properties and suitable for steam sterilization made from a thermoplastic resin composition having an aromatic polyester carbonate component and a component of polyalkylene terephthalate and/or a polyalkylene oxybenzoate.
U.S. Pat. No. 4,861,630 to Mihalich discloses that heat and impact resistant multilayered articles may be formed from thermoforming films obtained by co-extruding a layer of polycarbonate between two layers of polyester.
A hollow transparent delamination resistant heatset multilayer article is disclosed in U.S. Pat. No. 4,713,269 to Jabarin, et al. The article includes at least one high barrier layer containing a copolyester formed from terephthalic acid, ethylene glycol, 1,3 bis(2-hydroxyethoxybenzene), and, optionally, an amount of bis(4-beta-hydroxyethoxyphenyl)sulfone when it is necessary to raise the glass transition temperature for a particular application or use. A laminated structure of at least one layer of the high barrier copolyester directly adhered without adhesives to at least one layer of polyethylene terephthalate is disclosed. The PET materials disclosed as useful for forming the laminates of Jabarin, et al. are PET polymers including polymers where at least 97% of the polymer contains repeating ethylene terephthalate units with the remainder being minor amounts of ester-forming components, and copolymers of ethylene terephthalate wherein up to about 10 mole percent of the polymer is prepared from monomer units selected from butane-1,4-diol; diethylene glycol, propane-1,3-diol; poly(tetramethylene glycol); poly(ethylene glycol); poly(propylene glycol); 1,4-hydroxymethylcyclohexane and the like, substituted for the glycol moiety in the preparation of the polymer, or isophthalic; naphthalene, 1,4- or 2,6-dicarboxylic; adipic; sebacic; or decane-1,10-dicarboxylic acids, and the like, substituted for up to 10 mole percent of the acid moiety (terephthalic acid) in the preparation of the polymer. It is disclosed that the onset-of-shrinkage temperature for the high barrier copolyester/PET heatset container is essentially identical to that of a heatset PET monolayer container. Apparently the heat resistance of the container proposed by Jabarin, et al. results primarily from the heatsetting process and its effect on increasing the crystallinity in the PET layers. The heatsetting step is carried out at a temperature of 230xc2x0 C. for 10 seconds. The blow molded, heat-set containers are disclosed as having over 50% crystallinity and low haze.
A high barrier heatset intimate fusion blend article is disclosed in U.S. Pat. No. 4,713,270 to Jabarin, et al. The article is made from a blend of PET and the high barrier copolyester of Jabarin, et al. ""269 described above. It is disclosed that, in the heatsetting process, the PET in the fusion blended containers crystallizes very rapidly to a high crystallinity level in the presence of the high barrier copolyester. Thus, the copolyester acts as a crystallization promoter and increases the degree and rate of crystallization of the PET in the fusion blend, when compared to containers made solely of PET subjected to the same heatsetting conditions.
Another method of manufacturing preforms for blow molding heat resistant containers is disclosed in U.S. Pat. Nos. 5,443,766 and 5,464,106 and International Patent Application Number PCT/US95/08201 to Slat, et al. In the method, an insert is formed from one or more layers of thermoplastic, for example, by thermoforming flat sheets or forming a tubular coextrudate. The insert may contain a layer of heat resistant thermoplastic such as polyethylene naphthalate (PEN) or a blend of PEN and PET. The insert is placed into an injection mold and an outer layer of thermoplastic is injected to form the preform, which is then blow molded to form a multi-layer container. The thickness of the extruded intermediate layer of thermoplastic material may be varied, for example, to obtain a preform having a thinner layer of heat resistant material in the side walls and a thicker layer in the neck.
The co-processing of laminates containing more than one type of polymer may be difficult because of the different processing properties of the polymers. The optimum processing temperature for one polymer layer may create defects in the other layer during the processing of the laminate, and vice versa. For example, when multilayered preforms having a high Tg layer and at least one low Tg layer are processed (such as the PET/PEN/PET preforms disclosed in the Slat, et al. patents), defects may be created in the PET layers. The processing temperature for blow molding such a laminate is selected by considering the Tg of the PEN (high Tg) material. Generally the processing temperature is at least about the Tg of the high Tg layer, preferably at least 10-15xc2x0 C. greater than the Tg of the high Tg material, so that the high Tg material may be easily stretched. The processing temperature for a laminate having a PEN layer (Tgxc2x7123xc2x0 C.) is therefore at least about 135xc2x0 C. When the preform is heated to this processing temperature, the polyethylene terephthalate layer or layers thermally crystallize and whiten before the preform can be blow molded, causing unacceptable haze in the blow molded container and also affecting the drawing properties of the crystallized polyethylene terephthalate layer or layers.
Crystallization rate inhibitors for polyethylene terephthalate are disclosed in U.S. Pat. No. 4,415,727 to Toga, et al., U.S. Pat. No. 5,266,676 to Po"", et al. and U.S. Pat. No. 4,340,721 to Bonnebat, et al.
U.S. Pat. No. 4,415,727 to Toga, et al. discloses that it is important to minimize the crystallization of polyethylene terephthalate in the period between parison molding and blow molding and discloses a modified polyethylene terephthalate having 0.1 to 15 mol % of 2-methyl-1,3-propanediol as a glycol component of the PET to reduce crystallinity and the crystallization rate when blow molding thick walled bottles. U.S. Pat. No. 5,266,676 to Po"", et al., discloses 2,6-naphthalene dicarboxylic acid polyester resins with low crystallization speed. The polyesters may be used for the manufacture of bottles. U.S. Pat. No. 4,340,721 to Bonnebat, et al. discloses a polyester having 92.5% to 98.5% of ethylene terephthalate recurring units and 1.5 mole per cent to 7.5 mole per cent of a comonomeric crystallization retardant selected from one or more of the polybasic acids and/or polyhydric alcohols such as isophthalic, napthalenedicarboxylic, adipic and sebacic acids, or their ester forming derivatives. Exemplary diols disclosed are neopentyl glycol, hexane-1,6-diol, bis-1,4-hydroxymethylcyclohexane, diethylene glycol and triethylene glycol. U.S. Pat. No. 4,415,727, U.S. Pat. No. 5,266,676 and U.S. Pat. No. 4,340,721 do not disclose multi-layer laminates.
Another approach to providing a hot-fillable container is disclosed in U.S. Pat. No. 5,303,834 to Krishnakumar, et al. The blow molded, biaxially oriented container disclosed is squeezable with a paneled sidewall and preferably is able to receive a hot fill product without undergoing excessive shape distortion. The container may be made from a variety of thermoplastic materials including PET copolymer having 4-6% by total weight of a comonomer such as 1,4-cyclohexanedimethanol and/or isophthalic acid. Multi-layer containers are not disclosed.
A container having a PEN/PET core layer and PET outer layers is disclosed as suitable for hot-fill applications in Research Disclosure, vol. 294, No. 29410, October 1988, New York, N.Y., USA, pp. 714-719, XP 000068665, Disclosed Anonymously, Poly (Ethylene Naphthalenedicarboxylate)/Poly (Ethylene Terephthalate) Blends. The PEN/PET blends may contain from 1% to 99% PET. The material suitable as outer layer material is preferably a linear polyester such as PET or various commercially available versions thereof, such as PET modified with up to 50 mol percent of an aromatic or aliphatic dicarboxylic acid and/or up to 50 mol percent of an aliphatic glycol containing 3 to 12 carbon atoms.
U.S. Pat. Nos. 5,628,957 and International Patent Application Number PCT/US94/14350 to Collette, et al. disclose a multi-layer preform and container having a layer of a first polymer comprising PEN and a layer of a second polymer which remains substantially transparent after being stretched at a temperature above the orientation temperature of the first polymer. Various second polymer compositions are disclosed including: a PET low copolymer (0-2%); a PET high copolymer; a non-strain hardenable PET, or a non-strain hardenable blend or copolymer of PEN and PET copolymer; a PET copolymer having 30% cyclohexane dimethanol (PETG); a blend or copolymer of PETG and PEN; a mid-PEN polymer comprising 20-80% PEN and 20-80% PET; a high-PEN polymer comprising 80-100% PEN and 0-20% PET; and a high-PEN polymer comprising 80-100% PEN and 0-20% PET low copolymer.
It would be desirable to produce a co-processable multi-layer laminate having properties of high strength, transparency, low or no haze in the low cost, low Tg laminate layers, and furthermore, to produce such a laminate in a cost effective manner wherein the amount of high cost, high Tg materials are optimized to attain the desired end use properties of the laminate at the lowest possible cost. It would be desirable for such a laminate to have a high Tg layer having not only the desired end use properties of the laminate such as high barrier properties and/or heat resistance but also high strength. The high Tg material would be used in such proportion in the laminate wherein the laminate has the best properties of the high value, high Tg material without any excess used, thus achieving an optimized amount of the high Tg material.
It would also be desirable for such a laminate to have a low Tg layer having high strength, transparency and relatively no haze with crystallization rate inhibitors used in such proportion in the low Tg layer or layers of the laminate wherein the laminate has the best properties of the high value crystallization rate inhibitors without any excess being used, thus achieving an optimized amount of the crystallization rate inhibitors to attain both low or no haze and high strain induced crystallinity and accordingly high strength in the low Tg layer.
The present invention provides a co-processable multi-layer laminate having a high Tg layer and at least one low Tg layer. The layers have properties of high strength, lo- or no-haze, and transparency after processing into the form of a multi-layer sheet composition, an oriented film, a preform, a container including a food or beverage container, or another multi-layer structure. The present invention also provides methods of forming such laminate structures.
The multi-layer laminate has at least one low Tg layer comprising a first thermoplastic polyester, the first thermoplastic polyester comprising at least one crystallization rate inhibitor. The total amount of crystallization rate inhibitor is effective to prevent substantial haze in the low Tg layer upon heating the high Tg layer to a processing temperature above the Tg of the high Tg layer and stretching the laminate at the processing temperature, such that the at least one low Tg layer, after heating and stretching, is substantially transparent. Furthermore, in embodiments of the invention, the total amount of crystallization rate inhibitor does not substantially inhibit strain-induced crystallization of the at least one low Tg layer when the laminate is stretched at the processing temperature, such that the at least one low Tg layer, after heating and stretching, is substantially transparent and has high strength.
The present invention also provides multilayer structures that have a reduced amount of haze generated from thermal processing of crystalline thermoplastic polyesters in temperature ranges above their Tg. These multilayer structures also may exhibit strain induced crystallization when the structure is stretched, and the effective amount of crystallization inhibitor does not substantially inhibit the strain induced crystallization.
The present invention provides a co-processable multi-layer laminate having properties of high strength, transparency, low or no haze in the low cost, low Tg laminate layers, and furthermore, provides a laminate wherein the amount of high cost, high Tg materials are optimized to attain the desired end use properties of the laminate at the lowest possible cost, for example, in the case wherein the high Tg layer has desired end use properties such as high barrier properties, heat resistance, and high strength. The high Tg material is used in such proportion in the laminate wherein the laminate has the best properties of the high value, high Tg material without any excess used, thus achieving an optimized amount of the high Tg material.
The multilayer containers of the invention may provide improved properties such as reduced shrinkage and/or high barrier properties, with a very small amount of high Tg material used to impart the improved properties to the container.